JP6680949B2 - Method and apparatus for multiple access transmission - Google Patents

Description

  The present application relates to a method of signal transmission, and in particular to simultaneous transmission of multiple streams of multi-bit symbols.

  Sparse Code Multiple Access (SCMA) is a recently developed multiple user access scheme for telecommunications systems. In SCMA, multiple data bitstreams are encoded with each codebook consisting of multiple codewords. Each codeword is transmitted on one or more subcarriers of a block of SCMA subcarriers.

  The superposition of codewords on subcarrier blocks is transmitted by the network-side component when transmission occurs in the downlink direction from the network-side component to one or more user equipments (UEs). When transmission occurs in the uplink direction from two or more synchronized UEs to network-side components, each UE sends one or more codewords on a subset of subcarriers of the block of SCMA subcarriers assigned to that UE. Send. The network-side component receives signals in blocks of SCMA subcarriers from the two or more UEs that are superimposed on the radio interface channel between the two or more UEs and the network-side component.

  SCMA performance can be affected by various parameters, including codebook design.

According to one embodiment of the present disclosure, a method of signaling multiple streams of multiple bit symbols is provided. The method comprises, for each of the plurality of subcarriers, mapping ^{p × M} bits as constellation points in a 2 ^{p × M} point constellation, and transmitting the constellation points on the subcarriers. Including. The p × M bits include M bits of a k-bit symbol from each of the p streams of the plurality of streams. The variables p and M are positive integers.

  The step of transmitting constellation points on multiple subcarriers is performed for the downlink direction.

  In some embodiments, the M bits are equal to k, causing all of the bits of the multi-bit symbol to be mapped to more than one subcarrier of the plurality of subcarriers.

  In some embodiments, the M bits are equal to the number of bits (k) in the multi-bit symbol divided by the number of non-zero subcarriers (q) assigned per stream (k / q). , Each set of k / q bits of a multi-bit symbol is mapped to a different subcarrier.

  The method may further include, for each of the plurality of subcarriers, assigning a bit importance to each subset of k / q bits of the k-bit symbol from the p streams.

  The method may further include sorting the M bits from each of the p streams relative to each other based on the set of bit importance values assigned to each set of the M bits.

According to one embodiment of the present disclosure, an apparatus is provided that includes a processor and a computer-readable medium. A computer-readable storage medium stores computer-executable instructions that, when executed by a processor, perform the method of transmitting a multi-bit symbol from each of a plurality of streams on a set of subcarriers. The computer-executable instructions map, for each of the plurality of subcarriers, p × M bits as constellation points in a 2 ^{p × M} point constellation, and transmit the constellation points on the subcarriers. And performing the method including the steps of: The p × M bits include M bits of a k-bit symbol from each of the p streams of the plurality of streams. The variables p, M and k are positive integers.

According to one embodiment of the present disclosure, a method of signaling at least one stream of multi-bit symbols is provided. The method uses k / q bits as constellation points in a 2 ^{k / q-} point constellation for each of a plurality of subcarriers and for a total of K streams of p streams. Mapping and transmitting the constellation points on subcarriers. The k / q bits are a subset of k-bit symbols, and q is the number of non-zero subcarriers of the total number of subcarriers in the transmission resource allocated for the stream. Each subset of k / q bits is mapped to only one subcarrier. The variables K, k, p and q are positive integers.

  The step of transmitting constellation points on multiple subcarriers may be performed in the uplink or downlink directions.

  The method may further include, for each of the plurality of subcarriers, assigning a bit importance to each subset of k / q bits of the k-bit symbol from the p streams.

  The method may further include sorting the M bits from each of the p streams relative to each other based on the set of bit importance values assigned to each set of the M bits.

According to one embodiment of the present disclosure, an apparatus is provided that includes a processor and a computer-readable medium. The computer-readable storage medium stores computer-executable instructions that, when executed by a processor, perform the method of transmitting a multi-bit symbol from each of at least one stream on a plurality of subcarriers. The computer-executable instructions provide k / q bits for each of the plurality of subcarriers and for each of the p streams of the total K streams in a constellation in a 2 ^{k / q} point constellation. Is configured to perform a method comprising mapping as constellation points and transmitting the constellation points on subcarriers. The k / q bits are a subset of k-bit symbols, and q is the number of non-zero subcarriers of the total number of subcarriers in the transmission resource allocated for the stream. Each subset of k / q bits is mapped to only one subcarrier. The variables K, k, p and q are positive integers.

  Other aspects and features of this disclosure will be apparent to those skilled in the art upon reading the following description of various embodiments of this disclosure.

Embodiments are described below with reference to the accompanying drawings.
FIG. 2 is a block diagram of a Sparse Code Multiple Access (SCMA) multiplexing technique for multiple users. FIG. 6 is a block diagram of K layers of multi-bit symbols encoded and mapped to N subcarriers for downlink transmission, according to an aspect of the disclosure. FIG. 6 is a block diagram of 6 layers of 2-bit symbols encoded and mapped to 4 subcarriers for downlink transmission, according to an aspect of the disclosure. FIG. 6 is a block diagram of 6 layers of 2-bit symbols encoded for downlink transmission and mapped to 4 subcarriers according to an alternative aspect of the disclosure; Six user equipments each having a single layer of 2-bit symbols encoded for uplink transmission and mapped to two subcarriers of a set of four subcarriers according to an aspect of the disclosure. Equipment, UE) is a block diagram. Six user equipments each having a single layer of 2-bit symbols encoded for uplink transmission and mapped to two subcarriers of a set of four subcarriers according to an aspect of the disclosure. Equipment, UE) is a block diagram. FIG. 6 is a block diagram of 6 layers of 2-bit symbols encoded for downlink transmission and mapped to 4 subcarriers according to an alternative aspect of the disclosure; 6 is a graph of data comparing bit error rate (BER) performance of various access technologies in accordance with aspects of the disclosure. 6 is a graph of data comparing frame error rate (FER) performance of various access technologies in accordance with aspects of the disclosure. 6 is a flowchart illustrating a method of multiple access transmission for use in the downlink direction, according to one aspect of the disclosure. 6 is a flowchart illustrating a method of multiple access transmission for use in the uplink or downlink direction according to an aspect of the present disclosure. FIG. 6 is a block diagram of an apparatus for use in multiple access transmissions in the downlink direction, according to one aspect of the disclosure. FIG. 6 is a block diagram of an apparatus for use in multiple access transmission in the uplink or downlink direction according to one aspect of the present disclosure.

  It should be understood initially that although an illustrative implementation of one or more embodiments of the present disclosure is provided below, the disclosed system and / or method may be implemented using any number of techniques. . The present disclosure is in no way limited to the illustrative embodiments, including the designs and implementations shown and described herein, the drawings and the technology described below, but within the scope of the appended claims It can be changed according to all the equivalent ranges of the range.

  Code Division Multiple Access (CDMA) is a multiple access technique that spreads over a code sequence in which data symbols are orthogonal, a quasi-orthogonal code sequence, or a combination of both. Conventional CDMA coding is a two-step process in which a binary code is mapped to Quadrature Amplitude Modulation (QAM) symbols before a spreading sequence is applied. While conventional CDMA coding can provide relatively high data rates, new technologies and mechanisms to achieve even higher data rates are needed to meet the increasing demands of next generation wireless networks. Low Density Spreading (LDS) is a form of CDMA used to multiplex different layers of data. LDS uses repetitions of the same symbol in specific layers at non-zero positions in the time / frequency resource. As an example, in LDS Orthogonal Frequency Division Multiplexing (OFDM), the constellation points are repeated over the non-zero frequency tones of the LDS block. In Sparse Code Multiple Access (SCMA), a multidimensional codebook is used to spread the data across the tones, without the need for repeating symbols. In SCMA, the detection can be simplified because the multi-dimensional spreading codebook is sparse.

  An example 105 of a multi-layer SCMA non-orthogonal multiplexing technique is described with reference to FIG. Six bitstreams 110a, 110b, 110c, 110d, 110e, and 110f are shown, each encoded by one of the six SCMA codebooks 115, 115b, 115c, 115d, 115e, and 115f. ing. Each SCMA codebook outputs a respective SCMA codeword 112a, 112b, 112c, 112d, 112e, and 112f. SCMA codewords are mapped to transmission resources called SCMA blocks for transmission over the air interface. SCMA blocks are multiple layers across multiple transmit subcarriers (tone 1, tone 2, tone 3, tone 4). As shown in FIG. 1, each SCMA codeword includes each layer (layer 1, layer 2, layer 3, layer 4, layer 5) of each of the SCMA blocks (SCMA block 1 and part of SCMA block 2 are shown). , Layer 6) over multiple transmission subcarriers. The first SCMA codeword 120a extends across tones 1 and 2 of layer 1 of the first SCMA block. The second SCMA codeword 120b extends over tones 1 and 3 of layer 2 of the first SCMA block. The third SCMA codeword 120c is spread over tones 1 and 4 of layer 3 of the first SCMA block. The fourth SCMA codeword 120d extends across tones 2 and 3 of layer 4 of the first SCMA block. The fifth SCMA codeword 120e extends across tones 2 and 4 of layer 5 of the first SCMA block. The sixth SCMA codeword 120f extends across tones 3 and 4 of layer 6 of the first SCMA block.

A matrix form representation of the SCMA signal S encoded over a block of SCMA subcarriers is as follows:

The rows of the matrix represent the signal components to be transmitted on each subcarrier of the SCMA block of subcarriers, and the columns of the matrix represent the signal components to be transmitted on individual streams or layers. Each matrix entry is represented as s _i ^j (b ^(j) ), where the matrix entry is a function of the bits to be encoded. The subscript i is the subcarrier in which the bits are coded, the subscript j is the layer in which the bits are coded, and the variable b ^(j) is a vector representation of the multiple bits coded by the SCMA codebook. is there. An alternative representation of the signal mapped to each subcarrier of the SCMA block of subcarriers is included as follows:
s ₁ = s ₁ ⁽¹⁾ (b ⁽¹⁾ ) + s ₁ ⁽²⁾ (b ⁽²⁾ ) + s ₁ ⁽³⁾ (b ⁽³⁾ )
s ₂ = s ₂ ⁽¹⁾ (b ⁽¹⁾ ) + s ₂ ⁽⁴⁾ (b ⁽⁴⁾ ) + s ₂ ⁽⁵⁾ (b ⁽⁵⁾ )
s ₃ = s ₃ ⁽²⁾ (b ⁽²⁾ ) + s ₃ ⁽⁴⁾ (b ⁽⁴⁾ ) + s ₃ ⁽⁶⁾ (b ⁽⁶⁾ )
s ₄ = s ₄ ⁽³⁾ (b ⁽³⁾ ) + s ₄ ⁽⁵⁾ (b ⁽⁵⁾ ) + s ₄ ⁽⁶⁾ (b ⁽⁶⁾ )

  Certain aspects presented in this disclosure may be implemented for downlink transmissions from network-side components to one or more user equipments (UEs). Embodiments disclosed herein are for a network-side device to transmit one or more multi-bit symbols from each of multiple layers for each sub-carrier of a sub-carrier block for transmission to two or more UEs. It is considered to be the generation of SCMA, which generates a single constellation point from the bits of. Embodiments of the present disclosure show that, on a given subcarrier, instead of superimposing some codebook symbols, symbols generated using alternative coding and mapping schemes for those of the conventional SCMA codebook. Is considered to be the generation of SCMA.

  Certain aspects presented in this disclosure may be used for uplink transmissions from one or more UEs to network-side components. When aspects of this disclosure are implemented in the uplink direction, each UE maps at least one bit from one or more layers to a subset of subcarrier blocks. Two or more UEs jointly transmit on a subcarrier block. The signal component from the UE on each subcarrier is superimposed over the radio interface channel during transmission from the UE to the network side component.

  As shown in FIG. 1, SCMA uses a layer-specific codebook to encode bits for transmission on multiple subcarriers. Instead of using a codebook to generate symbols that are mapped to one or more multi-point constellations on one or more subcarriers, aspects of the present application encode one or more bits and these It provides for mapping the coded bits to one or more subcarriers as a multi-point constellation.

  A first embodiment of the present disclosure will be described below with reference to FIG. FIG. 2 encodes k-bit symbols from each of a subset of p layers out of a total of K layers and encodes the encoded bits into N L-point constellation mapping functions (210, 220). , 230, 240) to map to N subcarriers. FIG. 2 is considered to be an operation in which the network side device transmits to a plurality of client side UEs.

Each of the K layers (Layer 1, Layer 2, Layer 3, ..., Layer K) is shown to provide a symbol containing k bits (1, 2, ... K). Each layer may provide a stream such as a k-bit symbol when the network side device has data to send to its respective UE. In some implementations, a single layer is used for transmission to a single UE. In other implementations, multiple layers may be used for transmission to a single UE. All bits (1, 2, ..., K) of the layer 1 symbol 215 are routed to both the first L-point constellation mapping function 210 and the second L-point constellation mapping function 220. All bits (1, 2, ..., K) of the layer 2 symbol 225 are routed to both the first L-point constellation mapping function 210 and the N−1 th L-point constellation mapping function 230. . All bits (1, 2, ..., K) of the layer 3 symbol 235 are routed to both the first L-point constellation mapping function 210 and the (N−1) th L-point constellation mapping function 230. . All the bits of the layer K-2 symbol 245 are routed to both the second L-point constellation mapping function 220 and the N-th L-point constellation mapping function 240. All the bits of symbol 255 of layer K-1 are routed to both the second L-point constellation mapping function 220 and the N-th L-point constellation mapping function 240. All bits (1, 2, ..., K) of the layer K symbol 265 are routed to both the N−1th L-point constellation mapping function 230 and the N-th L-point constellation mapping function 240. . In the scenario above where the k binary bits from the p layers are combined by the L-point constellation mapping function, the number L equals 2 ^{k * p} .

  Each L-point constellation mapping function 210, 220, 230, 240 receives p sets of bits, each set from a different layer. The combination of the p sets of bits forms a multi-bit symbol that is mapped to points in the L-point constellation by an L-point constellation mapping function. The manner in which the p sets of bits are arranged in the multi-bit symbol is implementation specific. In some embodiments, the placement of the set of bits within the multi-bit symbol is based on the assigned importance level of the individual set of bits. The use of importance levels assigned to a set of bits can help mitigate errors in decoding the bits at the receiver.

  The placement of the set of bits in the multi-bit symbol affects the location of the points mapped by the L-point constellation mapping function. In the particular example where 2-bit symbols from each of the three different layers are combined, the result is a 6-bit symbol. Bits 1 and 2 of the 6-bit symbol (2 bits from the first layer) have the highest significance at the position of the point in the L point mapping, and bits 3 and 4 (2 bits from the second layer). Bits 1 and 2 are considered to have lower importance at the point position and bits 5 and 6 (2 bits from the third layer) have the lowest importance at the point position It may have a higher protection against errors and bits 5 and 6 may have a lower protection against errors. Placing a set of bits of a multi-bit symbol such that the set of bits of a given layer cannot be assigned the lowest importance within different subcarriers provides for protection of the bits against errors between different layers. Can help provide level fairness.

3 is similar to FIG. 2 but is combined by a specific value associated with the number of bits per symbol on a given layer, the total number of layers of bits, each multi-point constellation mapping function. 2 shows an example having the number of layers of bits, the number of subcarriers, and the number of points in the constellation mapping. In FIG. 3, there are 6 layers of 2 bit symbols (layer 1, layer 2, layer 3, layer 4, layer 5, layer 6). The three layers of 2-bit symbols are combined with each of the multi-point constellation mapping functions (310, 320, 330, 340). The result of combining the two bits from the three layers is a 6-bit symbol. As a result, the multi-point constellation mapping function maps 6-bit symbols as 2 ⁶ = 64-point constellations.

The representation of the 6-bit symbol as a function of the bits from 3 of the 6 streams mapped to 4 subcarriers is as follows:
s ₁ = s ₁ (b ⁽¹⁾ , b ⁽²⁾ , b ⁽³⁾ )
s ₂ = s ₂ (b ⁽¹⁾ , b ⁽⁴⁾ , b ⁽⁵⁾ )
s ₃ = s ₃ (b ⁽²⁾ , b ⁽⁴⁾ , b ⁽⁶⁾ )
s ₄ = s ₄ (b ⁽³⁾ , b ⁽⁵⁾ , b ⁽⁶⁾ )

The variable b ^(j) is a vector representation of the set of bits for the jth layer (j = 1-6).

  Referring to FIG. 3, a bit pair 305 of Layer 1 symbols is routed to both a first 64-point constellation mapping function 310 and a second 64-point constellation mapping function 320. The bit pair 315 of the layer 2 symbol is routed to both the first 64-point constellation mapping function 310 and the third 64-point constellation mapping function 330. The bit pair 325 of the layer 3 symbols is routed to both the first 64-point constellation mapping function 310 and the fourth 64-point constellation mapping function 340. The bit pair 335 of the layer 4 symbols is routed to both the second 64-point constellation mapping function 320 and the third 64-point constellation mapping function 330. The bit pair 345 of the layer 5 symbols is routed to both the second 64-point constellation mapping function 320 and the fourth 64-point constellation mapping function 340. The bit pair 355 of the layer 6 symbol is routed to both the third 64-point constellation mapping function 330 and the fourth 64-point constellation mapping function 340.

  Each 64-point constellation mapping function 310, 320, 330, 340 receives bit pairs from three different layers. The combination of these three bit sets forms a 6-bit symbol that is mapped to a 64-point constellation by the respective 64-point constellation mapping function. As mentioned above, the placement or ordering of the bit pairs that are combined into 6-bit symbols for transmission on each subcarrier is done in order to support fairness between layers and to reduce errors at the receiver. Good based on importance.

  The 64-point constellation mapping function may use, for example, quadrature amplitude modulation (QAM) or phase shift keying (PSK) as a part of the mapping function.

  In a second embodiment applicable to the downlink, instead of combining multi-bit symbols from multiple layers in each of multiple sub-carriers, a subset of bits of the multi-bit symbols from each layer are different It is separately mapped to subcarriers. An example is shown below with reference to FIG.

FIG. 4 shows an example of 6 layers, each having a symbol of 2 bits. Instead of the bit pairs in a symbol being routed together to two multi-point constellation mapping functions, each bit of the symbol in each layer is routed to a different multi-point constellation mapping function, as in FIG. One bit is mapped to only one subcarrier. Each multi-point constellation mapping function receives one bit from three different layers. Since the single bits from each of the three layers are combined by the multi-point constellation mapping function, the number of bits in the multi-bit symbol mapped to the multi-point constellation is 1 bit x 3 layers = 3 Is a bit. As a result, the number of points in the multi-point constellation is 2 ³ = 8. Therefore, for each respective sub-carrier, the 3-bit symbol is mapped into an 8-point constellation.

  Referring to FIG. 4, the first bit 405a from layer 1 is routed to the first 8-point constellation mapping function 410 and the second bit 405b from layer 1 is routed to the second 8-point constellation mapping function 420. To be done. The first bit 415a from layer 2 is routed to the first 8-point constellation mapping function 410 and the second bit 415b from layer 2 is routed to the third 8-point constellation mapping function 430. The first bit 425a from layer 3 is routed to the first 8-point constellation mapping function 410 and the second bit 425b from layer 3 is routed to the fourth 8-point constellation mapping function 440. The first bit 435a from layer 4 is routed to the second 8-point constellation mapping function 420 and the second bit 435b from layer 4 is routed to the third 8-point constellation mapping function 430. The first bit 445a from layer 5 is routed to the second 8-point constellation mapping function 420 and the second bit 445b from layer 5 is routed to the fourth 8-point constellation mapping function 440. The first bit 455a from layer 6 is routed to the fourth 8-point constellation mapping function 440 and the second bit 455b from layer 6 is routed to the third 8-point constellation mapping function 430.

  The placement of the individual bits, which are combined into a 3-bit symbol for transmission on each subcarrier, helps to ensure fairness of reconstruction between layers and to reduce errors at the receiver. Good based on assigned importance.

The representation of the 3-bit symbol as a function of the bits from 3 of the 6 streams mapped to 4 subcarriers is as follows:
s ₁ = s ₁ (b ₁ ⁽¹⁾ , b ₁ ⁽²⁾ , b ₁ ⁽³⁾ )
s ₂ = s ₂ (b ₂ ⁽¹⁾ , b ₁ ⁽⁴⁾ , b ₁ ⁽⁵⁾ )
s ₃ = s ₃ (b ₂ ⁽²⁾ , b ₂ ⁽⁴⁾ , b ₂ ⁽⁶⁾ )
s ₄ = s ₄ (b ₂ ⁽³⁾ , b ₂ ⁽⁵⁾ , b ₁ ⁽⁶⁾ )

The variable b _m ^(j) is an expression of the m-th bit (m = 1 to M, M = 2) of the j-th layer (j = 1 to 6).

  FIG. 4 shows an example of 6 layers, each having 2 bit symbols. The bits from each layer are coded with the bits from two other examples and then three bits are mapped to one of four subcarriers. However, it should be understood that each of the above values is generalized. For example, the number of layers can be represented by K layers, the number of bits in each layer can be represented by k bits, and the total number of layers that can be routed to the constellation mapping function is K. The number of bits in the subset of bits from each of the p layers of the layers that are routed to a particular constellation mapping function can be represented as k / q bits, where q Is the number of non-zero valued subcarriers for which the bits of a given layer are transmitted, and the constellation mapping function has L points, where L = (k × p) / q. When k / q is not an integer value, the total number of bits in a given layer symbol can be divided into q bit groups. Since some groups contain more bits than others, the allocation of q bit groups may change on different subcarriers in different resource blocks to maintain the fairness level.

  The third embodiment of the present disclosure may also encode a subset of bits of a multi-bit symbol from one or more layers and separately map these encoded subsets of bits to different individual subcarriers. set to target. An example of the uplink is shown below with reference to FIGS. 5A and 5B, and an example of the downlink is shown below with reference to FIG. 5C.

  A first example for the uplink is described below with reference to Figures 5A and 5B. 5A and 5B show that six UEs 502, 512, 522, 532, 542, and 552 each deploy a multi-bit symbol from a single layer into an assigned subset of a set of subcarriers in a transmission resource. An example of encoding is shown. In the particular example of FIGS. 5A and 5B, each UE is assigned two subcarriers of the set of four subcarriers. The signals transmitted on the respective subcarriers by the six UEs are superimposed on the respective subcarriers during transmission via the radio interface between the UE and the network side device.

  It should be appreciated that if a UE is not assigned to a particular subcarrier of a set of subcarriers for transmission at a given time, then no signal is transmitted by that UE on that subcarrier. The UE may be assigned different subsets of the set of subcarriers at different times. It should be further understood that although the examples of FIGS. 5A and 5B include 6 UEs, the number of UEs may be more or less than 6 based on a given implementation of the process described herein.

In the particular UE of FIGS. 5A and 5B, each data bit of the 2-bit symbol is only routed to a single multi-point constellation mapping function to map to only one subcarrier. In the particular example of FIGS. 5A and 5B, since only a single bit from a single layer is routed to the multi-point constellation mapping function, the number of bits mapped by the multi-point constellation mapping function is 1 bit × 1 layer = 1 bit. As a result, the number of points in the multipoint constellation is 2 ¹ = 2. Therefore, for each respective subcarrier, a single bit is mapped into a two-point constellation.

  Referring again to FIGS. 5A and 5B, the first UE 502 is transmitting a stream of 2-bit symbols to a network side device (not shown). The first bit 505a from the 2-bit symbol is routed to the first 2-point constellation mapping function 510a and the second bit 505b from the 2-bit symbol is routed to the second 2-point constellation mapping function 510b.

  At the second UE 512, the first bit 515a from the 2-bit symbol is routed to the first two-point constellation mapping function 520a and the second bit 515b from the two-bit symbol is routed to the third two-point constellation mapping function 520c. To be done.

  At the third UE 522, the first bit 525a from the 2-bit symbol is routed to the first two-point constellation mapping function 530a and the second bit 525b from the two-bit symbol is routed to the fourth two-point constellation mapping function 530d. To be done.

  At the fourth UE 532, the first bit 535a from the 2-bit symbol is routed to the second two-point constellation mapping function 540b, and the second bit 535b from the two-bit symbol is routed to the third two-point constellation mapping function 540c. To be done.

  At the fifth UE 542, the first bit 545a from the 2-bit symbol is routed to the second two-point constellation mapping function 550b and the second bit 545b from the two-bit symbol is routed to the fourth two-point constellation mapping function 550d. To be done.

In a 6UE552, first bit 555a from 2-bit symbols are routed to the fourth two-point constellation mapping function 560d, the second bit 555b from 2-bit symbol routed to the third two-point constellation mapping function 560c To be done.

A matrix form representation of the collective signals transmitted from the 6 UEs of FIGS. 5A and 5B is as follows:

The rows of the matrix represent the signal components to be transmitted on each subcarrier and the columns of the matrix represent the signal components to be transmitted on the individual layers. In particular, in this case, the columns correspond to individual UEs, since each UE has only a single stream. Combined matrix entries in the 6 columns of the matrix may be transmitted on each of the subcarriers and represent values from 6 UEs. Each matrix entry is represented as s _i ^j (b ^(j) ). Where the matrix entry is a function of the bits to be coded, i is the subcarrier on which the bits are coded, j is the layer (UE) on which the bits are coded, b _m ^(j) (M = 1 or 2) are the individual bits to be encoded. Alternative representations of the signal mapped to each subcarrier are included as follows:
s ₁ = s ₁ ⁽¹⁾ (b ⁽ ₁ ¹⁾ ) + s ₁ ⁽²⁾ (b ₁ ⁽²⁾ ) + s ₁ ⁽³⁾ (b ₁ ⁽³⁾ )
s ₂ = s ₂ ⁽¹⁾ (b ₂ ⁽¹⁾ ) + s ₂ ⁽⁴⁾ (b ₁ ⁽⁴⁾ ) + s ₂ ⁽⁵⁾ (b ₁ ⁽⁵⁾ )
s ₃ = s ₃ ⁽²⁾ (b ₂ ⁽²⁾ ) + s ₃ ⁽⁴⁾ (b ₂ ⁽⁴⁾ ) + s ₃ ⁽⁶⁾ (b ₂ ⁽⁶⁾ )
s ₄ = s ₄ ⁽³⁾ (b ₂ ⁽²⁾ ) + s ₄ ⁽⁵⁾ (b ₂ ⁽⁵⁾ ) + s ₄ ⁽⁶⁾ (b ₁ ⁽⁶⁾ )

  Since each UE transmits only a selected subset of sub-carriers, the above matrix and equations for individual sub-carriers are a set of those transmitted by all UEs, rather than by any one UE individually. Expression.

  The UE may have the processing power to implement multiple multi-point constellation mapping functions to enable the processing that the signal is mapped to each of the subcarriers assigned to the UE. 5A and 5B show a plurality of two-point constellation mapping functions, each dedicated to a particular subcarrier, while FIGS. 5A and 5B show in order to clearly show the particular subcarriers the UE transmits and does not transmit, 1 is an example used to describe one embodiment of the present application. In other implementations, multiple multi-point constellation mapping functions that are not dedicated to a particular subcarrier and thus can be used to map one or more layers to be transmitted by a UE to any assigned subcarrier. There is good.

  5A and 5B show an example of 6 UEs each having a 2-bit symbol and each having a single layer. Each bit of each 2-bit layer is separately coded and mapped to only one respective subcarrier. However, it should be understood that each of the above values can be generalized. For example, the number of layers can be represented by K layers, the number of bits in each layer can be represented by k bits, and the total number of layers that can be routed to the constellation mapping function is K. The number of bits in the subset of bits from each of the p layers of the layers that are routed to a particular constellation mapping function can be represented as k / q bits, where q Is the number of non-zero valued subcarriers for which the bits of a given layer are transmitted, and the constellation mapping function has L points, where L = (k × p) / q. When k / q is not an integer value, the total number of bits in a given layer symbol can be divided into q bit groups. Since some groups contain more bits than others, q bit group assignments may be generated on different subcarriers in different resource blocks to maintain fairness levels.

  Furthermore, although FIGS. 5A and 5B show that each UE transmits only a single layer, it should be understood that this should not be considered as a limitation. One or more UEs of the UE group that are transmitting together to the network side device may have more than one layer of multi-bit symbols to transmit.

  In a scenario where a UE transmits multiple layers, a multi-point constellation mapping function that maps to subcarriers assigned to the UE receives a subset of bits of a k-bit symbol from each of the layers that the UE transmits. For example, if a UE transmits two layers, each multi-point constellation mapping function that maps to subcarriers allocated for use by the UE may have k / q bits from each of the two layers. Receive different subsets. Where q is the number of non-zero valued subcarriers over which the bits for a given layer are transmitted. It should be taken into account that in order to correctly decode the bits at the receiver, a method of distinguishing the bits of a given layer is needed. Therefore, bits from different layers that are coded on the same subcarrier may need to be coded with different coding schemes or possibly with different capability levels to distinguish the new composite.

  Another example for the downlink is described below with reference to FIG. 5C. FIG. 5C illustrates an example where network-side device 570 encodes multi-bit symbols from each of multiple layers into a set of subcarriers. FIG. 5C is similar to FIG. 4 in that there are 6 layers, each layer having 2-bit symbols, and that 2 bits of each layer are separately mapped to different subcarriers of the set of subcarriers. Is. However, in FIG. 4, for a single subcarrier, the individual bits from each of the three layers are combined and encoded as a 3-bit symbol by an 8-point constellation mapping function. On the other hand, in FIG. 5C, for a single subcarrier, each of the three bits from three different layers is each encoded by a two-point constellation mapping function. The result of these three coded bits is mapped to subcarriers.

  The first bit 572a from layer 1 is routed to the first two-point constellation mapping function 585a and the second bit 575b from layer 1 is routed to the fifth two-point constellation mapping function 590b. The first bit 574a from layer 2 is routed to a third two-point constellation mapping function 585c and the second bit 574b from layer 2 is routed to a seventh two-point constellation mapping function 594a. The first bit 576a from layer 3 is routed to the second two-point constellation mapping function 585b and the second bit 576b from layer 3 is routed to the twelfth two-point constellation mapping function 596c. The first bit 578a from layer 4 is routed to the fourth two-point constellation mapping function 590a and the second bit 578b from layer 4 is routed to the eighth two-point constellation mapping function 594b. The first bit 580a from layer 5 is routed to the sixth two-point constellation mapping function 590c and the second bit 580b from layer 5 is routed to the tenth two-point constellation mapping function 596a. The first bit 582a from layer 6 is routed to the eleventh two-point constellation mapping function 596b and the second bit 582b from layer 6 is routed to the ninth two-point constellation mapping function 594c.

  The outputs from the two-point constellation mapping functions 585a, 585b, and 585c are all mapped to subcarrier 1 and are therefore superposed before transmission by the network side device. The outputs from the two-point constellation mapping functions 590a, 590b, and 590c are all mapped to subcarrier 2 and are therefore superposed before transmission by the network side device. The outputs from the two-point constellation mapping functions 594a, 594b, and 594c are all mapped to subcarrier 3 and thus superposed before transmission by the network side device. The outputs from the two-point constellation mapping functions 596a, 596b, and 596c are all mapped to subcarrier 4 and are therefore superposed before transmission by the network side device.

  FIG. 5C shows an example of 6 layers, each having 2 bit symbols. The two bits in each layer are coded separately and then mapped to two of the four available subcarriers in the transmission resource. However, it should be understood that each of the above values can be generalized. For example, the number of layers can be represented by K layers, the number of bits in each layer can be represented by k bits, and the total number of layers that can be routed to the constellation mapping function is K. The number of bits in the subset of bits from each of the p layers of the layers that are routed to a particular constellation mapping function can be represented as k / q bits, where q Is the number of non-zero valued subcarriers for which the bits of a given layer are transmitted, and the constellation mapping function has L points, where L = (k × p) / q. When k / q is not an integer value, the total number of bits in a given layer symbol can be divided into q bit groups. Since some groups contain more bits than others, q bit group assignments may be generated on different subcarriers in different resource blocks to maintain fairness levels.

<Performance evaluation>
For purposes of describing the performance of some embodiments of the present application for a particular parameter set, an exemplary simulation is described with reference to Figures 6A and 6B.

  Simulations were performed for 4 different multiple access technologies. The first technique is a conventional SCMA technique with a specific codebook design. The simulation conditions for the first technique were applied in the downlink direction and consisted of a signal structure of 6 layers with 2 bits per symbol per layer mapped to a set of 4 subcarriers. The second technique is a first embodiment of an application of the kind described with reference to Figures 2 and 3. Here, all bits of a 2-bit symbol for a given layer are mapped to two subcarriers, and bits from all layers are collectively mapped to a total of four subcarriers of transmission resources. It This simulation condition for the second technique was also applied in the downlink direction and consisted of a signal structure of 6 layers with 2 bits per symbol per layer mapped to a set of 4 subcarriers. The third technique is a second embodiment of an application of the kind described with reference to Figures 5A and 5B. Here, different bits of a 2-bit symbol of one layer are mapped to different respective subcarriers, and each bit of the layer is mapped to only one subcarrier. The simulation conditions for the third technique were applied in the uplink direction and consisted of signal configurations of 6 UEs transmitting a single layer, each having 2 bits per symbol. Each UE maps different bits of the 2-bit symbol to different subcarriers of the subset of two subcarriers assigned to the UE from a total of four subcarriers in the transmission resource. The fourth technique is a third embodiment of the type of application described with reference to FIG. The simulation conditions for the fourth technique were applied in the downlink direction and consisted of a signal structure of 6 layers with 2 bits per symbol per layer. Different bits of the 2-bit symbol are mapped to different respective subcarriers of the set of 4 subcarriers in the transmission resource.

The following parameters were used in the simulation:
Additive White Gaussian Noise (AWGN) channel;
Quadrature Phase Shift Keying (QPSK) modulation;
Turbo code, rate = 1/2;
Frame length = 576;
Number of UEs = 6;
Number of samples (tones, symbols) = 4;
Overload = 150%.

  Simulation results are shown in Figures 6A and 6B. FIG. 6A shows the Bit Error Rate (BER) plotted on the y-axis against the signal-to-noise ratio (in dB) for each of the four techniques. FIG. 6A shows the Frame Error Rate (FER) plotted on the y-axis against the signal-to-noise ratio (in dB) for each of the four techniques.

ここで：
Ｎは、サブキャリア数；
Ｎ_ｉｔは、デコーダで実行される必要のある反復の数；
ｋは、レイヤ毎のシンボル当たりのビット数；
ｐは、サブキャリア当たりにマッピングされるレイヤの数；
ｑは、送信リソースの中のサブキャリアの総数のうち、各レイヤによる使用のために割り当てられた非ゼロサブキャリアの数である。 The following table summarizes, for each technique in the simulation, the link direction in which the technique is used, the gain in dB (relative to conventional SCMA), and the approximate complexity associated with each technique.

here:
N is the number of subcarriers;
N _it is the number of iterations that need to be performed at the decoder;
k is the number of bits per symbol for each layer;
p is the number of layers mapped per subcarrier;
q is the number of non-zero subcarriers allocated for use by each layer of the total number of subcarriers in the transmission resource.

  FIG. 7 is a flow chart illustrating an example of a method 700 performed by an apparatus on a network side of a communication system for transmitting multi-bit symbols from each of multiple streams on a set of subcarriers. In some implementations, the apparatus may be a base station or co-located with a base station.

The following steps are performed for each of the plurality of subcarriers assigned for transmission by the network side device. In a first optional step 710, the network-side device assigns a bit importance to each set of M bits from each of the p streams of the multiple streams of multi-bit symbols. At subsequent optional step 720, the network-side device sorts the M bits from each of the p streams relative to each other based on the assigned importance of each set of M bits. At step 730, the network device maps the ^{p × M} bits as constellation points in the 2 ^{p × M} point constellation. The p × M bits include M bits of a k-bit symbol from each of the p streams of the plurality of streams, where p, M, and k are positive integers. In step 740, the device transmits constellation points on subcarriers.

  In some implementations of method 700, the number M of bits is equal to the number k of bits in the symbol. In this case, all bits of the multi-bit symbol are mapped to more than one sub-carrier of the sub-carriers. An example of such an implementation corresponds to FIG.

  In some implementations of method 700, the number of bits M is equal to the number of bits k in the symbol divided by the number of nonzero subcarriers assigned per stream, q, and k / q of k-bit symbols. Each subset of the set of bits is mapped to a different subcarrier. An example of such an implementation corresponds to FIG.

  In some implementations, when the optional step 710 is performed, each set of M bits is of importance so that the M bits cannot be assigned the lowest importance in more than one constellation point mapping. Assigned to.

  FIG. 8 is a flowchart illustrating an example method 800 that may be performed in the downlink or uplink directions. In the downlink direction, the network-side device transmits multi-bit symbols from at least one of the multiple streams on multiple subcarriers. In the uplink direction, a client-side device in a communication system transmits multi-bit symbols from at least one of multiple streams on multiple subcarriers.

The following steps are performed for each of the plurality of subcarriers assigned for transmission. In a first optional step 810, the client-side device assigns a bit importance to each subset of bits of the k-bit symbol from each of the p streams. At optional step 820, the client-side device sorts the subsets of bits from each of the p streams relative to each other based on the assigned importance of each subset of bits. At step 830, for each of the p streams of the total K streams, the client-side device maps the ^{k / q} bits as constellation points in a 2 ^{k / q} constellation. . Where q is the number of non-zero subcarriers in the total number of subcarriers in the transmission resources allocated for the stream, and each subset of k / q bits is mapped to only one subcarrier. It The variables p and k are positive integers. In step 840, the client-side device sends the constellation points on the subcarriers.

  In the situation where the client-side device sends a single stream, the value of p is equal to 1. An example of this is shown for each of the four UEs in FIG.

FIG. 9 is an example of a device 900 at a network side of a communication system configured to implement aspects of the present disclosure. The device 900 includes a processor 920 and a computer-readable storage medium 930. Computer readable storage media 930 include computer executable instructions 935 configured to, when executed by processor 920, transmit a multi-bit symbol from each of a plurality of streams on a set of subcarriers. Computer-executable instructions 935, when executed by processor 920, are configured to map ^{p × M} bits for each of the plurality of subcarriers as constellation points in a 2 ^{p × M} point constellation. It The p × M bits include M bits of a k-bit symbol from each of the p streams of the plurality of streams. The variables p, M and k are positive integers. Computer-executable instructions 935, when executed by processor 920, are further configured to, for each of the plurality of subcarriers, transmit a constellation point on the subcarrier. Computer-executable instructions 935 assign a bit importance to each set of M bits from each of the p streams of the plurality of streams of multi-bit symbols, such as, but not limited to, Computer-executable instructions 935 may also be included to implement other functionality such as sorting the M bits from each of the p streams relative to each other based on the assigned importance of each set.

  Device 900 may be part of, or co-located with, the base station and provide the base station with an encoded signal for transmission over the set of subcarriers.

  FIG. 10 is an example of a client-side device 1000 of a communication system configured to implement aspects of the present disclosure. The equipment may be part of a UE that is one of many UEs that communicate with a network side device. As described above with reference to the example of FIG. 5, multiple UEs may transmit to the network side device on a subset of the set of subcarriers.

The device 1000 includes a processor 1020 and a computer-readable storage medium 1030. Computer-readable storage medium 1030 includes computer-executable instructions 1035 configured to, when executed by processor 1020, transmit a multi-bit symbol from each of the at least one stream on a plurality of subcarriers. The computer-executable instructions 1035, when executed by the processor 1020, generate k / q bits of 2 ^k for each of the plurality of subcarriers and for each of the p streams of the total of K streams. ^{It is} configured to map as constellation points in the ^{/ q-} point constellation. Where q is the number of non-zero subcarriers in the total number of subcarriers in the transmission resources allocated for the stream, and each subset of k / q bits is mapped to only one subcarrier. It The k / q bits include k / q bits of a k-bit symbol from each of the p streams of the at least one stream, where p and k are positive integers. Computer-executable instructions 1035, when executed by processor 1020, are further configured to, for each of the plurality of subcarriers, transmit a constellation point on the subcarrier. Computer-executable instructions 1030, for example and without limitation, assign a bit importance to each bit of the symbol from each of the p streams of the at least one stream of multi-bit symbols, each set of k bits. Computer-executable instructions 1035 may be included to implement other functionality, such as sorting bits from each of the p streams relative to each other based on their assigned importance.

Many modifications and variations of the present disclosure are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the present disclosure may be practiced other than as specifically described herein.

Claims (22)

A method of transmitting a signal of a plurality of streams of a plurality of bit symbols, wherein the plurality of bit symbols includes k bits, the plurality of streams includes K streams, and k is an integer of 2 or more, K is a positive integer, and the method is
For each of the N subcarriers, N is a positive integer,
Mapping p × M bits as constellation points in a 2 ^{p × M} point constellation, said p × M bits of p streams of said K streams. Comprising M bits of k-bit symbols from each, p is an integer greater than or equal to 2 less than K, and M is a positive integer;
Transmitting the constellation points on the N subcarriers;
Including the method.   The step of transmitting the constellation point on the N subcarriers comprises the step of a network-side component transmitting the streams of multi-bit symbols on the N subcarriers in the downlink direction. The method according to 1.   3. When M = k, any of the k bits included in the multi-bit symbol is mapped to more than one subcarrier of the plurality of subcarriers. The method described in.   Each set of k / q bits of the multi-bit symbol is mapped to a different subcarrier, where M = (k / q) and q is the number of non-zero subcarriers allocated per stream. 3. The method according to any one of claims 1 and 2.   The step of mapping the p × M bits is based on a set of bit importance assigned for each set of M bits, the M bits from each of the p streams relative to each other. The method according to any of claims 1 to 4, further comprising the step of sorting. For each of the N subcarriers,
Assigning bit importance to each set of M bits from the p streams,
The method of claim 5, further comprising:   Assigning the bit significance to each set of M bits assigns to each set of M bits such that the M bits cannot be assigned the lowest significance in more than one constellation point mapping. 7. The method of claim 6 including assigning the bit importance. A device,
A processor,
A computer-readable medium having computer-executable instructions stored thereon, the computer-executable instructions, when executed by the processor, comprise multi-bit symbols from each of a plurality of streams. A computer-readable medium for performing the method of transmitting on N subcarriers;
And the multi-bit symbol includes k bits, the plurality of streams includes K streams, k is an integer greater than or equal to 2, and K is a positive integer, and the method comprises:
Mapping p × M bits as constellation points in a 2 ^{p × M} constellation for each of the N subcarriers, the p × M bits being the K Of M-bits of the k-bit symbol from each of the p-streams of the stream, p, the variable p is an integer greater than or equal to 2 less than K, and M and N are positive integers, Steps,
Transmitting the constellation points on the N subcarriers;
Equipment, including.   9. The device of claim 8, wherein the device is a network-side component that transmits the streams of multi-bit symbols on the N subcarriers.   10. When M = k, all of the k bits included in the multi-bit symbol are mapped to more than one subcarrier of the plurality of subcarriers. Equipment described in.   Each set of k / q bits of the multi-bit symbol is mapped to a different subcarrier when M = (k / q) and q is the number of non-zero subcarriers allocated per stream. Item 10. The device according to any one of items 8 to 9. The computer-executable instructions, when executed by the processor,
Assigning a bit importance to each set of k bits from each of the p streams of the multiple streams of multi-bit symbols,
The apparatus according to claim 8, further comprising: The computer-executable instructions, when executed by the processor,
sorting k bits from each of the p streams with respect to each other based on the assigned bit importance of each set of k bits,
13. The device of claim 12, further comprising: A method of transmitting a signal of at least one stream of multi-bit symbols, said multi-bit symbols comprising k bits, k being an integer greater than or equal to 2, said method comprising:
For each of the N subcarriers, N is a positive integer,
For each of the p streams of the total K streams, p is an integer greater than or equal to 2 and less than K, and K is a positive integer,
Mapping k / q bits as constellation points in a 2 ^{k / q-} point constellation, said k / q bits being a subset of k-bit symbols, q being assigned to said stream Of non-zero subcarriers out of the total number of subcarriers in the allocated transmission resource, k and q are positive integers, and each subset of k / q bits is mapped to only one subcarrier. , Step,
Transmitting the constellation points on the N subcarriers;
Including the method.   Transmitting the constellation point on the N subcarriers comprises a user equipment (UE) transmitting the at least one stream of k-bit symbols on q subcarriers in the uplink direction. The method according to claim 14.   16. The method of claim 15, wherein the q subcarriers are a subset of N subcarriers allocated as transmission resources for transmission in the uplink direction by multiple UEs including the UE.   The at least one stream has a number of streams ≧ 2, and the step of mapping the p bits is based on an assigned set of bit importance of each set of bits from each of the p streams. 17. A method according to any of claims 14 to 16, further comprising the step of sorting the individual bits with respect to each other. For each of the N subcarriers,
Assigning bit importance to each subset of k / q bits of the k-bit symbol from the p streams,
18. The method of claim 17, further comprising:   The step of assigning the bit importance to each subset of k / q bits of the k-bit symbol is such that all bits from the k-bit symbol are not assigned the lowest importance in a constellation point mapping with more than one. 19. The method of claim 18, further comprising assigning the bit importance to each subset of k / q bits. A device,
A processor,
A computer-readable medium having computer-executable instructions stored thereon, the computer-executable instructions, when executed by the processor, a multi-bit symbol from each of at least one stream. A computer-readable medium for performing the method of transmitting on multiple subcarriers,
Wherein the multi-bit symbol includes k bits, k is an integer greater than or equal to 2, the plurality of subcarriers includes N subcarriers, N is a positive integer, and the method comprises:
For each of the N subcarriers,
For each of the p streams of the total K streams, p is an integer greater than or equal to 2 that is less than K, and K is a positive integer,
Mapping k / q bits as constellation points in a 2 ^{k / q-} point constellation, said k / q bits being a subset of k-bit symbols and q being a Is a number of non-zero subcarriers out of the total number of subcarriers in the transmission resource allocated for k and q are positive integers, and each k / q bit subset maps to only one subcarrier Step,
Transmitting the constellation points on the N subcarriers;
Equipment, including. The computer-executable instructions, when executed by the processor,
Assigning bit importance to each subset of k / q bits of a k-bit symbol from each of the p streams of the at least one stream of multi-bit symbols,
Further executing the apparatus according to claim 20. The computer-executable instructions, when executed by the processor,
sorting the subsets of k / q bits from each of the p streams relative to each other based on the assigned bit importance of each set of k bits;
22. The device of claim 20 or 21 , further comprising:

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